In an exclusive interview, Arabo "BK" Babakhani tells Anderson Cooper what happened when his roommate at the University of Central Florida, James Oliver Seevakumaran, confronted him with a gun before Seevakumaran took his own life.

Babakhani immediately slammed and locked the door and called 911. "I was definitely scared, but calm, I was just taking cover in my room behind objects ... so that if he did fire, he wouldn't be able to hit me" he says.

By the time law enforcement arrived and raided the dorm, the 30 year old was dead.

Police say surveillance video and evidence found in Seevakumaran's room indicate he was in the final stages of carrying out an attack on the campus. Authorities recovered a checklist outlining his plot, weapons, ammunition, and homemade bombs.

Babakhani describes the would-be gunman as "anti-social" and says they were not friends. Hear more about their relationship and the frightening incident in the interview.